The sensing of agricultural crops including tree foliage for controlling the amount of chemicals to be applied is well known to improve upon the economics of care as well minimizing the adverse impact on the environment. As described in the U.S. Pat. No. 4,823,268 to Giles et al., issued in 1989, tremendous strides have been made in agricultural production. However, the ever-increasing cost of chemical materials, such as fertilizers, insecticides, herbicides, and the like, as well as the constraints from government authorities regarding their use, has prompted considerable research with a goal of improving the efficiency of agricultural material application.
In an orange grove or orchard, for example, knowledge of the size and shape of a target area based on an actual measurement is most desirable for the application of the chemical materials. Sensing devices have been developed using ultrasonic technology as described in the Giles '268 patent referred to above. In addition, sensing systems have employed a plurality of sensors, as described in U.S. Pat. No. 4,768,713 to Roper, for actuating a plurality of spray nozzles used to distribute the wet chemical materials to be applied. However, improved accuracy in the measurement of various shapes can be achieved by using the narrow beam available with a laser rangefinder, as described in U.S. Pat. No. 5,278,423 to Wangler, et al., which discloses a continuously scanning pulsed laser radar beam from a single rangefinder sensor operable with a mobile agricultural sprayer that moves between trees in a grove or orchard to determine the foliage on the tree to be targeted and estimates a tree height based on the highest pulse returned, the disclosure of which is herein incorporated by reference. By way of example, the Wangler '423 sensor allows zone-controlled spraying while optimizing water and chemical usage thus minimizing soil and ground water pollution. Only a pre-selected amount of spray, determined to be necessary to cover the foliage, is dispensed by the sprayer, thus eliminating wasted spray above and between crops. Desirably, an eye-safe laser is used for accurately detecting the presence and extent of foliage on each side of the agricultural sprayer for automatically activating the sprayer controls to limit spraying only to the foliage. There is also a need for such accuracy in determining characteristics such as the center of the tree, the density of the foliage within the target, foliage volume with the canopy of the tree, density of the canopy, and the like for locating and characterizing the tree within the plurality of trees being treated. Combining this information with other inputs, a grower will be able to make more timely and accurate estimates of crop production. Further, there is a need to map agricultural fields without the high dependency on weather conditions and the high cost of aerial photography.